Radio-frequency identification (RFID)-based tracing is becoming increasingly common in many fields of trade and industry. Although many industrial sectors have utilized tracing systems, covering the product chain from the supplies of raw materials to the final products in the market, the forestry and wood sector is still in the beginning of this process partly due to a complicated supply chain structure. The nature of logging operation itself, logistics of the forest industry, environmental factors, needs of the user of the logs and the demanding electromagnetic properties of wood set special requirements for the transponder application process and transponders itself, only to mention some aspects. The general objective in this sector is to develop methodology and advanced technologies that can improve the use of wood and optimize the forest production through the chain of transformation, minimizing environmental impacts (www.indisputablekey.com).
Two main types of RFID transponders (tags) are known that can be used for marking logs (http://www.indisputablekey.com/transponder_applicator.php): a patch type transponder, which is inserted into a slot or groove machined into the log, and a nail type transponder, which is inserted into a hole drilled into the wood or hammered directly into the wood. Patch transponders typically have the form of a rectangular slab. However, an additional machining step is undesirable because it slows down and increases the complexity of the marking process and requires expensive special tools. In addition, the transponder may come loose and drop from the log during transportation, for example. On the other hand, a nail-type transponder hammered into the wood has the disadvantage that the antenna of the transponder is buried deep into the wood material and the casing of the transponder has to be manufactured from a very hard and strong material. In practise, it has been found that it is difficult to manufacture a nail-type transponder which is sufficiently strong to be directly nailed into wood. Some examples of nail-type transponders are described in GB 2294846 and the article “Transponders for Timber Management”, Skip Garrett, United States Department of Agriculture, Forest Service, Forest Management Tech Tips, March 1997.